1. Field of the Invention
The present invention relates to an image reading apparatus capable of detecting a dot pattern formed according to a predetermined period, and to an image forming apparatus having an image reading apparatus of this kind.
2. Description of the Related Art
A method is known in which security is imparted to a printed matter by synthesizing pattern image data with document data created by a computer, inside an image forming apparatus such as a printer. In addition to a pattern image which is formed as a dot pattern and causes a warning text such as “COPY” to emerge when the image duplicated, there is also a pattern image which can embed output information, such as printer information, the print date, and so on, as an electronic watermark. It can be considered that by printing a pattern image of this type, security processing of some kind can be applied to the document, and therefore it is possible to restrict illegal reproduction or illicit procurement of a original document.
Moreover, a copying machine comprising a copy guard function is known, in which, if a mask pattern which incorporates a special dot pattern is printed together with a document image, and it is then sought to duplicate the original document, copying of the document is prohibited by means of the copying machine recognizing the dot pattern, or alternatively, rather than printing the document, a solid image pattern, for example, is formed so as to prevent leaking of the information in the document.